The present invention relates to a continuous ion exchange processes for water softening and for mineral recovery. More particularly, the present invention relates to a closed loop method employing regenerable liquid ion exchange materials for the treatment of aqueous feedwater streams containing dissolved minerals such as salts of sodium, calcium, magnesium, copper and zinc, amongst others.
It is well known that it is desirable to remove mineral species from aqueous solutions prior to certain uses. In particular, it is desirable to remove those mineral species which contribute to hard water problems in household water utilization. In particular, hard water is known to have a deleterious effect on detergents used for the washing of clothes and dishes. Moreover, hard water problems also contribute to the formation of scale in pipes and hot water heaters. It is also known that it is desirable to remove certain mineral ion species from aqueous solutions either for the purpose of recovering the mineral or for the purpose of removing an undesirable mineral containment. Accordingly, it is seen that it is desirable to remove such mineral species as sodium, calcium, magnesium, copper and zinc amongst others from aqueous solutions for one or more of the reasons stated above.
One of the methods presently employed for such mineral removal utilizes solid, thermally regenerated ion exchange resin processes which have been developed using solid resin ion exchange materials. However, processes involving such solid ion exchange materials must be operated in a batch mode and furthermore can require complex control methodologies for absorption, regeneration and rinse operations. In other, more conventional ion exchange processes, ion exchangers which are loaded with ions are regenerated by reacting with an acid, a base or a salt. This regeneration process has the disadvantage that it adds chemicals to the treated solution and therefore has a higher operating cost as a result of the consumption of chemical regenerating materials. In certain cases, the addition of chemicals to the treated water is undesirable.
Accordingly, it is seen that it would be desirable to have a continuous process for ion exchange purposes. More particularly, it would be desirable to have a process in which the ion exchange material is continuously recycled without the necessity for chemical additives to regenerate the liquid ion exchange material to an operationally desirable state.